Double Beta Decay of ⁴⁸Ca

⁴⁸Ca, the lightest experimentally accessible double beta decay candidate, is the only one simple enough to be treated exactly in the nuclear shell model. Thus the ββ₂ᵥ half-life measurement, reported here, provides a unique test of the nuclear physics involved in the ββ matrix element calculation. Enriched ⁴⁸Ca sources of two different thicknesses have been exposed in a time projection chamber. We observe a half-life of T²ᵛ₁/₂ = (4.3⁺².⁴₋₁.₁[stat] ± 1.4[syst]) × 10¹⁹ yr consistent with shell model calculations.